Arp 194: Evidence of Tidal Stripping of Gas and Cross-Fueling

We present new imaging and spectroscopic observations of the interacting system Arp 194 (≡UGC 6945 ≡ VV 126). The northern component (A194N) is a distorted spiral or ring galaxy likely disrupted by a collision or close encounter with a southern galaxy (A194S). There is evidence that a third galaxy with similar recession velocity is projected on A194N, but its role is likely secondary. A194S is connected to A194N by a string of emission knots, which motivates our interpretation that the former was the intruder. Three of the knots are easily discernible in B, R, and Hα images and are assumed to trace the path of the intruder following the encounter, which we estimate occurred a few times 108 yr ago. Both A194S and A194N are experiencing strong bursts of star formation: the Hα luminosity indicates a total star formation rate ~10 M⊙ yr-1. The lack of detectable J and K emission from the blobs, along with strong Hα emission, indicates that an evolved stellar population is not likely to be present. The brightest knot (closest to A194S) shows a star formation rate of ≈1.2 M⊙ yr-1, which, if sustained over a time ≈7 × 107 yr, could explain the spectral energy distribution. This suggests that the stripped matter was originally predominantly gaseous. The brightest knot is detected as a FIRST radio source, and this is likely the signature of supernova remnants related to enhanced star formation. Motions in the gas between the brightest knot and A194S, traced by an emission line link of increasing radial velocity, suggests infall toward the center of the intruder. Arp 194 is therefore one of the few galaxies where evidence of "cross-fueling" is observed.